Tomato yield in the Kleingartenanlage Dreieck Nord. Left: control bed fertilized with nettle manure. Right: bed fertilized with urine-based C.R.O.P.® fertilizer. Picture: KGA Dreieck Nord
11 August 2023
The human "waste" urine holds great potential for the recovery of the plant nutrients nitrogen and phosphorus. Although it accounts for only 1 percent of the total volume, it is responsible for 70-80 percent of the nitrogen and 45-60 percent of the phosphorus found in wastewater. Separate urine collection in special toilets or urinals and targeted processing to produce recycling fertilizer makes this valuable resource accessible.
In the C.R.O.P.® project (Combined Regenerative Organic food Production) of the DLR Institute of Aerospace Medicine (DLR - Institut für Luft- und Raumfahrtmedizin - Bioregeneration), a filter system for urine recycling was developed which produces a mineral fertiliser with a high nitrogen content. This product of the C.R.O.P.® filter system can fertilise vegetables growing in a greenhouse. This is of great importance for long-term missions to the moon or Mars, as the amount of supplies that can be transported to a planetary base is limited. If waste streams like urine are used to produce food, nutrients are recycled and missions can be extended.
The C.R.O.P.® fertilizer is produced from urine in a biological process. The fertiliser is odourless. Picture: DLR
A scientific experiment at the Leibniz Institute of Horticulture and Ornamental Crops (IGZ) (IGZ - Leibniz-Institut für Gemüse- und Zierpflanzenbau) has shown that human waste is well suited as fertiliser (Evaluating recycling fertilizers for tomato cultivation in hydroponics, and their impact on greenhouse gas emissions). In the experiment, growing vegetables with fertilisers made from human faeces and urine was as productive as using conventional fertiliser. No risk of disease transmission was found, and the heavy metal load was even lower than in common mineral fertilisers.
Following the experiments in a scientific setting, the IGZ coordinated the Citizen Science Project Urban Cycles (Urban Cycles), which investigated whether recycled fertiliser made from human urine also works under real conditions in hobby gardens. Gardeners tested DLR's C.R.O.P.® fertiliser in their vegetable beds and evaluated their observations in dialogue with the researchers. A total of 14 garden teams from community, school and private gardens in Berlin and the surrounding area fertilised their vegetables with recycled fertiliser made from synthetic urine for one gardening season. As a control, a similar bed section was fertilised as usual. The fertilisation techniques in the control beds differed individually: some gardeners fertilised with nettle manure or horn shavings, others with compost or not at all. Compared to unfertilised control beds, cultivation with the C.R.O.P.® fertiliser produced more yield. Compared to fertilised control beds, the yield with the C.R.O.P.® fertiliser was the same or higher. The good dosability of the recycling fertiliser probably played a significant role here, because in contrast to the C.R.O.P.® fertiliser, the nutrient contents of nettle manure or compost are not known to the gardeners preventing precise dosage.
Currently, the use of recycling fertilisers made from human urine is not allowed in agricultural and horticultural practice either in Germany or in the EU. Therefore, the Urban Cycle experiments were conducted with a fertiliser made from synthetic urine. The experiments of the IGZ showed that urine-based fertilisers have a similar effect to other fertilisers and at the same time have much lower heavy metal loads. Therefore, the Urban Cycles project was also meant to initiate a socio-political debate in which the use of human waste products as fertilisers in food production is discussed by consumers.